A typical tank-style, gravity flow toilet comprises a tank and a bowl. The purpose of the tank is to receive and store a quantity of water for flushing the toilet. A ball cock assembly is disposed in the tank, and includes an inlet tube that allows water under pressure to flow into the tank, to a predetermined level (quantity). A water supply line is connected to the ball cock assembly. A flush valve is disposed in the tank and, when operated, allows the quantity of water stored in the tank to be delivered to the bowl for flushing the toilet. A typical flush valve is a "flapper-type" flush valve, including a disc-like "flap" which closes off an end of a discharge pipe. A flush lever controls the operation of the flush valve. The bowl sits atop a sewage pipe. A seat and lid are disposed atop the bowl.
FIG. 1 illustrates an exemplary flapper-type flush valve 100 of the prior art, the structure and operation of which is well known. The flush valve 100 comprises an upper flapper body portion 102 and a lower float member portion 104. The flapper body portion 102 is generally in the form of a disc, having an upper surface 102a and a lower surface 102b. The float member portion 104 extends from the lower surface 102b of the flapper body portion 102. A pair of generally parallel, spaced-apart arms 106 extend in a rearward direction from a rearward position (right hand side, as viewed) of the flapper body portion 102. A hole 108 is provided in a distal end of each arm 106 for pivotally securing the flush valve 100 to a corresponding pair of pins or trunnions 110 extending from an overflow pipe 112. The trunnions 110 are disposed at diametrically-opposed positions on an outer surface of the overflow pipe 112. The rearward-extending arms 106 and trunnions 110 extending through the holes 108 serve to position and align the flush valve 100, and to guide the flush valve 100 as it moves between a "closed" position and an "open" position.
In FIG. 1, the flush valve 100 is illustrated as being in a "closed" position. In this closed position, the lower surface 102b of the flapper body portion 102 sealingly engages a top end 114a of a discharge pipe (flush outlet) 114, the top end of the discharge pipe 114 functioning as a valve seat. The discharge pipe 114 has a diameter sufficiently large that the float member portion 104 fits easily within the bore of the discharge pipe 114. The float member portion 104 also helps to center the flapper body portion 102 on the top end 114a of the discharge pipe 114.
A chain (e.g., ball chain or "S" chain) or strap 116 extends from a flush lever lift arm (not shown) to a mounting lug 118 which is disposed on the front (left, as viewed) of the flapper body portion 102, generally diametrically-opposed to the rearwardly-extending arms 106. When the flush lever lift arm is momentarily operated depressed, the chain 116 pulls upward on the flush valve 100, causing the flapper body portion 102 to move away from the top end 114a of the discharge pipe 114, thereby "opening" the flush valve 100. In this "open" position, water (not shown) in the toilet tank (not shown) is allowed to flow into the toilet bowl (not shown) to "flush" the toilet. As the water level in the toilet tank is replenished, at the end of the flush cycle, the flush valve 100 automatically returns to its "closed" position.
The float member portion 104 is cup-shaped, defining an air chamber 120. The air chamber 120 is typically sized to contain 2.25 to 2.50 cubic inches of air. An opening 122 is provided at the base of the float member portion 104. In use, when the flush valve 100 is opened, the buoyancy of the air inside the air chamber 120 assists in maintaining the flush valve 100 in the open position until the water level drops below the float member portion 104, at which time the weight of the flapper body portion 102 causes the flush valve to drop and close.
The flapper body portion 102, float member portion 104, rearwardly-extending arms 106 and the mounting lug 118 are typically integrally formed of a resilient material, such as soft rubber or an elastomer. In the event of a failure of only a portion of such an integrally-formed flush valve 100, the entire flush valve 100 would need to be replaced. The discharge pipe 114, the top end 114a of which serves as a valve seat for the flush valve 100, is a part of the toilet, not a part of the flush valve 100.
The operation of a tank-style, gravity flow toilet, such as has been described with respect to FIG. 1, is generally well known. The tank typically holds (stores) anywhere from about 1.6 gallons to about 8 gallons of water. When the water in the tank is released by opening the flush valve, the first few gallons of water are forced into the toilet bowl by volume and weight of the remaining water in the tank. As the water flows through the toilet bowl and down into the sewer drain, it creates a suction which pulls all the waste and water from the toilet bowl, assisted by ambient air pressure. This method of eliminating liquid or solid waste from the toilet bowl is referred to as "siphon jet action". The siphon jet action only requires a few gallons to work efficiently. The balance (remainder) of the water in the toilet tank serves to generate the force and velocity to drive the first few gallons from the toilet tank into the toilet bowl with sufficient force to sustain the siphon jet action.
Typical tank-style gravity-flow toilets (3.5 gallons or larger) use substantially all of the water that is stored in the toilet tank to flush the toilet bowl. It has been recognized that this practice is somewhat wasteful, and has contributed to a sewage waste water problem. Government regulations have been directed to reducing the quantity of water that a toilet may use to flush waste from the toilet bowl. Currently, most states have adopted regulations that require toilets used in new construction to use no more than 1.6 gallons of water per flush. However, there are millions of older style toilets in use that use 3.5 gallons, or more, of water per flush.